All AP Physics 2 Resources
Example Questions
Example Question #231 : Ap Physics 2
What was a result of Young's double slit experiment?
Light was demonstrated to have properties consistent with both particles and waves.
Light, when separated by two slits, turns back into a single beam when observed.
None of the answers are correct.
Light is actually solely a wave, and the Corpuscular Theory of Light was wrong.
Light is solely comprised of particles, called photons.
Light was demonstrated to have properties consistent with both particles and waves.
Young's Double Slit Experiment is famous because it demonstrated that light, theretofore thought of as solely discrete particles called corpuscles, actually had properties of waves in addition to particles. This was demonstrated by the two light beams separated by the note card used by Young constructively and destrucively interfering with each other to form bands of light and darkness, which showed that light acts like a wave. However, the light that reached the wall was made up of discrete points, which could only occur if light also could behave like it was made of particles. Therefore, it was concluded that light can act both like a particle and a wave, known as wave-particle duality.
Example Question #2 : Slit Experiments
Red light (wavelength ) is sent through a double slit. The slits are apart. The light then hits a screen which is behind the double slit. How far is the first bright fringe from the second bright fringe?
This question is just a quick application of the double slit formula.
, where is the distance the bright fringe is from the center of the screen. is the wavelength, is the distance the slit is from the center of the screen, and is the slit width. If you set , the value of you get is also the distance between each adjacent bright fringe (the first and second are adjacent).
Note-The value we got is very large because of the very small slit width.
Example Question #1 : Other Wave Concepts
Consider an electromagnetic wave travelling through a vacuum. If the magnetic field's wave is , and the speed of light is , what is the strength of the electric field?
There is not enough information to determine the strength of the electric field wave
In an electromagnetic wave, the electric and magnetic portions are proprtional to each other. The ratio of electric field to magnetic field is , the speed of light.
Using this information, we can determine the strength of one part given the other.
We have and , so now we multiply the two.
Therefore, the strength of the electric field is .
Example Question #2 : Other Wave Concepts
Consider an electromagnetic wave travelling through a medium where the speed of light is . If the strength of the electric field is , and the speed of light is , what is the magnetic field strength?
In an electromagnetic wave going through a vacuum, the ratio of and is the speed of light, ; however, this relation doesn't change when light goes through a medium. The ratio still is the speed of light, but instead of , it's the speed of light through the medium. Therefore, for velocity ,
In this problem, we're told that the speed of light through the medium is , so if we rearrange the equation to solve for and use in place of v, we'll get our answer.
Therefore, the strength of the magnetic field is .
Example Question #1 : Other Wave Concepts
Which of the following electromagnetic waves has the longest wavelength?
Radio waves
Gamma rays
Microwaves
X-rays
Visible light
Radio waves
Wavelength is indirectly related to the amount of energy in the wave (the frequency). The most energetic wves are gamma rays, while the least energetic are radio waves. This means that radio waves have the longest wavelength.
A helpful mnemonic for remembering the order of wavelengths in the electromagnetic spectrum from longest to shortest is "Raging Martians invaded Roy G Biv using x-ray guns."
In order, the letters stand for
- Radio
- Micro
- Infrared
- Red
- Orange
- Yellow
- Green
- Blue
- Indigo
- Violet
- Ultraviolet
- X-ray
- Gamma
Example Question #231 : Ap Physics 2
When light refracts through a medium, which of the following quantities does not change?
Index of refraction of the medium
Average speed of the wave
All of these quantities change during refraction
Frequency of the light
Wavelength of the light
Frequency of the light
When light is refracted, the average speed is lower if the index of refraction is higher (and vice versa). In order to refract, the medium light travels through must have a changing index of refraction. Because the amount of energy the light carries must be constant during refraction, the frequency (which is proportional to energy) cannot change. Therefore, since and the frequency must stay the same when the speed changes, wavelength must also change.
Example Question #234 : Ap Physics 2
A circular radar antenna on a boat has a diameter of and has a frequency of . Two smaller boats are located from the boat. How close can the smaller boats be and still be detected as two objects?
When trying to find the minimum distance between two objects that makes them still distinguishable, we use the Rayleigh criterion equation.
is the minimum angle at which two objects can be resolved, is the wavelength of the wave being used, and is the diameter of the circular aperture (in this case, the antenna would be the aperture). An important part of equations like these is the small-angle approximation, which states, as the angle approaches zero,
This means that, if the angle is small enough, . In our problem, we're trying to find , so we can substitute for
Next, since we're not given the wavelength, but we are given the frequency, we can find the wavelength using the following equation:
Now, solve for .
Example Question #2 : Other Wave Concepts
Determine the frequency of light of wavelength .
None of these
Using
Where is the speed of light, is frequency and is wavelength
Converting to and plugging in values
Solving for
Example Question #5 : Other Wave Concepts
Suppose that you're sitting at the beach one day, and you realize that the waves are hitting the shore once every 5 seconds. If you also know that the peaks of the waves are 15 meters apart, what is the speed of the incoming waves?
For this question, we're given the distance between wave peaks (wavelength) as well as how long it takes for each wave to hit the shore (period). We're then asked to use this information to solve for the speed of the waves.
First, we'll need to use an equation for the speed of a wave.
We know from the question stem that we have the wavelength, which is the distance between the peaks of each wave. But we do not have the frequency. However, we can solve for frequency by using the period of the wave as follows:
Which we can alternatively write as:
The period of the wave, , represents the amount of time it takes for a single wave to pass a given point, and thus has units of time. The inverse of this quantity is the frequency, which describes how many waves pass by a given point in a certain amount of time. Usually, the unit of time in these cases is seconds.
Thus, for every one second that passes, one-fifth of a wave will pass by any given point.
Now, we can plug this value into the equation for the speed of the wave to solve for our answer:
Example Question #232 : Ap Physics 2
As you gradually turn down the light on a dimmer switch, you notice that it shows a red glow the instant before it turns off. Why does this happen?
Compared to other colors, red light travels through air slower.
Compared to other colors, red light travels through air faster.
Compared to other colors, red light has more energy.
Compared to other colors, red light has less energy.
Compared to other colors, red light has less energy.
To answer this question, let's first recall that on the visible spectrum, red light has the longest wavelength. Due to this, red light also has the lowest energy. We can show this with the equation
As the dimmer is gradually turned down, less and less energy is being provided to the light bulb. Consequently, since red light has the least amount of energy of all the colors on the visible spectrum, we briefly see red light the instant before the light turns off completely. Note that the speed of a wave is determined by the medium. In this case, regardless of the wavelength, the medium is air, which determines the speed of any electromagnetic wave.
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